The present invention relates to a method for manufacturing, for example, active matrix type liquid crystal display and thin-film transistors (hereinafter called "TFT") to be used for these devices.
FIG. 4 shows a cross-sectional drawing showing a process for manufacturing conventional TFT array substrates with TFT of the TFT type liquid crystal display in which low-resistivity bus lines are provided. In the drawing, numeral 1 denotes a transparent insulating substrate such as glass substrate, etc., 2 a gate electrode formed on the transparent insulating substrate 1, 3 a gate line formed on the transparent insulating substrate 1, 4 a gate insulating film formed on the gate electrode 2 and the gate line 3, 8 a semiconductor layer formed on the gate electrode 2 via the gate insulating film 4, 9 an ohmic contact layer formed on the semiconductor layer 8, 10 a pixel electrode, 11 a hole for connecting with a terminal, formed on the gate insulating film 4 on the gate line 3, 12 a source-drain electrode formed on the ohmic contact layer 9, 13 a channel, and 14 a passivation film.
Next description will be made on the process for manufacturing the conventional TFT array substrate on which TFTs are provided. As shown in FIG. 4(a), after forming a single-layer film made of a low resistivity metal such as Al or Al alloy, etc. on the surface of the transparent insulating substrate 1, patterning is carried out using a photoresist formed by photolithography process, and the gate electrode 2 and gate line 3 are formed. Then, as shown in FIG. 4(b), silicon nitride is formed to be a film by plasma enhanced CVD method and the gate insulating film 4 is formed. Then, as shown in FIG. 4(c), after continuously forming amorphous silicon film by plasma enhanced CVD method and n.sup.+ type amorphous silicon film which is doped with impurities, using a photoresist formed by photolithography process, the amorphous silicon film and n.sup.+ type amorphous silicon film are simultaneously patterned, and the semiconductor layer 8 and ohmic contact layer 9 are formed at the position above the gate electrode.
Then, as shown in FIG. 4(d), after ITO (indium tin oxide) film is formed as a transparent conductive film, using a photoresist formed by photolithography process, the ITO film is patterned to form the pixel electrode 10. Then, as shown in FIG. 4(e), the gate insulating film 4 on the gate line 3 is removed by etching, and a hole 11 for providing the terminal is formed. Then, as shown in FIG. 4(f), after forming Cr, etc. to be a film, using a photoresist formed by photolithography process, the film is patterned and the source-drain electrode 12 and the source signal conductor are formed on the ohmic contact layer 9. This is followed by removal of the n.sup.+ type amorphous silicon film (ohmic contact layer 9) of the portion not covered with the source drain electrode 12 by dry etching to form the channel 13, and then, the photoresist is removed. Lastly, as shown in FIG. 4(g), silicon nitride is formed to be a film and passivation film 14 is formed.
As described above, with the conventional TFT array substrate, the gate electrode 2 and gate line 3 are formed with the film primarily comprising metals with low resistivity, such as Al, etc. but because these metals provide poor chemical resistance, an etchant used for patterning the ITO film composing the pixel electrode 10 penetrates through the portion lacking of film in the gate insulating film 4 and corrodes the gate electrode 2 and the gate line 3, raising problems of lowering the yield and reliability of TFT.
Hitherto, for a method to prevent corrosion of conductors composing the gate electrode 2 and gate line 3 caused by the etchant attacking the ITO film, a method to perform an anodic oxidation of conductors of Al film, etc. composing the gate electrode 2 and gate line 3 to form oxide film on their surfaces has been proposed.
For example, in Japanese Unexamined Patent Publication No. 183897/1992, there is proposed a method for forming an anodic oxidation film 18 on the gate electrode 2 and gate line 3 other than the areas coated with photoresist 17 by forming the gate electrode 2 and gate line 3 by patterning after first forming single-layer film by metals with low resistivity such as Al or Al alloys on the surface of the transparent insulating substrate 1 as shown in FIG. 5(a), and anodic oxidation after forming the photoresist 17 for protecting the portion serving as a region for taking out terminals on the gate line 3 as shown in FIG. 5 (b). Because with this method, the anodically oxidized film 18 is not formed in the region for providing terminals of the gate line 3, if terminals are connected with the gate line 3, the process for removing the anodic oxidation film in the region is not required.
In Japanese Unexamined Patent Publication Nos. 110749/1989, 217378/1992, and 323304/1993, first of all, a single-layer film is formed with metals with low resistivity such as Al or Al alloys, on the surface of the substrate 1a as shown in FIG. 6(a), then, the film is patterned to form the first conductive film 2a, and then, the first insulating film 4a is formed on the first conductive film 2a using insulation material or high-resistivity semiconductor material as shown in FIG. 6(b). In this event, as shown in FIG. 6(c), in the first insulating film 4a, film lacking portion 5a is generated. Then, there is proposed a method for forming an insulating film or oxide film 19 at a lacking portion 5a of a film by electrophoresis or anodic oxidation as shown in FIG. 6(d). With this method, it is possible to form the insulating film or the oxide film 19 selectively only on the lacking portion 5a of the film generated in the first insulating film 4a.
As described above, several methods have been hitherto proposed as a method for preventing penetration of the etchant used for patterning of ITO film composing the pixel electrode 10 in the conventional TFT type liquid crystal display in which low resistivity bus lines are provided and for preventing corrosion of the gate electrode 2 and gate line 3 formed by the material with low resistivity such as Al, etc. through the lacking portion, etc. in the gate insulating film 4, but any of them are not effective.
For example, in the method for forming the anodic oxidation film 18 on the surfaces by anodic oxidation after forming the gate electrode 2 and gate line 3, photoresist 17 must be formed to prevent the oxide film 18 from being formed on the area (area for taking out terminals) in contact with the upper layer via the insulating film, raising problems of reducing the productivity, etc.
Because in the method for forming the insulating film or oxide film 19 selectively only on the film lacking portion 5a in the first insulating film 4a after forming the first insulating film 4a on the first conductive film 2a, the insulating film or oxide film 19 are formed by electrophoresis, anodic oxidation process, or other methods without carrying out pretreatment after the first insulating film 4a is formed, the potential defective portion of the film such as dust taken into the first insulating film 4a is actualized, raising a problem of generating another film lacking portion.
This invention has been made to solve the problems as mentioned above, and it is object of the present invention to provide the provision of a process for manufacturing high-reliability thin-film transistors without lowering productivity and with enhanced yield by preventing corrosion of gate electrode and gate line resulting from the etchant attacking the ITO film composing the pixel electrode without forming any protective film by the photolithography process newly and disposing of the potential lacking portion of the film by actualizing the portion in advance.
It is another object of this invention to provide a liquid crystal display of a high aperture ratio by forming patterns with fine lines by composing the gate electrode and gate line by the use of material with low resistivity.